Blood filter

ABSTRACT

A device for treating human blood prior to its return to a living human body. The blood filter employs a bed of particles between about 50 and 1,000 microns in size, the outer surface of which particles is formed of impermeable carbon. Suitable spheres may be coated with vapor-deposited pyrolytic carbon, and the particles may be supported between upper and lower screens which are likewise coated.

[ 1 Aug. 26, 1975 ploys a microns pheres may be Diefendorf Beatty etKrakauer et United Kingdom.................

ABSTRACT 1/1960 Hutcheon........................ 10/1963 10/1969 10/1972Agent, or Firm-Fitch, Even, Tabin &

11 Claims, 2 Drawing Figures FOREIGN PATENTS OR APPLICATIONS 344,502

Primary Examiner-Samih N. Zaharna Assistant Examiner-Ivars CintinsAttorney, Luedeka A device for treating human blood prior to its returnto a living human body. The blood filter em bed of particles betweenabout 50 and 1,000 in size, the outer surface of which particles isformed of impermeable I carbon. Suitable s coated with vapor-depositedpyrolytic carbon, and the particles may be supported between upper andlower screens which are likewise coated.

128/214 C; 210/506; 210/DIG. 23 BOld 23/14 210/36, 39,

, 214 C, DIG. 3

210/500 210/266 210/DIG. 23 210/510 z k N \-..\.W-\

n w m mo yr RM Inventor: Jack C. Bokros, San Diego, Calif.

Assignee: General Atomic Company, San Diego, Calif.

Feb. 25, 1974 Appl. No.: 445,112

us. 210/263; 128/214 R- 128/DIG. 3; 210/436; 210/500 R' Int. Field ofSearch.............

510, DIG. 23, 503, 504; 128/214 R References Cited UNITED STATES PATENTS8/1948 Wickenden......................... 10/1951 Cahan.............

United States Patent Bokros BLOOD FILTER [22] Filed:

BLOOD FILTER This invention relates to the filtration of blood and moreparticularly to an improved filter for use in an extracorporeal bloodcirculation circuit.

Various types of blood filters have been developed for use in theextracorporeal circulation of the blood, particularly in connection witha heart-lung machine, with a kidney machine, or with other types ofbloodpump or assist devices. Examples of some such blood filters areshown in U.S. Pat. Nos. 3,448,041, and 3,593,854. Blood filters may alsobe used to filter blood which is being transfused from storage to aliving body.

It is the general objective of such blood filters to remove microembolifrom blood being returned to a living human being, and a discussion ofthe potential dangers to a patient which can be alleviated by the use ofblood filtering is set forth in an article entitled Platelet-LeukocyteEmboli-- Origins, Effects & Treatment that appeared in the Fall, I973issue of The Journal of Extra-Corporeal Technology, Volume V, Number 4,pp. 23-33. v

Presently available blood filters are not considered to be entirelysatisfactory. Although they have been considered to have been effectiveto remove certain microemboli from the bloodstream, these filters arealso considered to create other problems which are believed to inurefrom their inherent incompatibility with blood. The disadvantage isthat, even though an ideal filter may be designed for the removal ofpreexisting microemboli, if thrombogenic materials are used in itsconstruction, the filter can alter the protein and other elements ofblood so that emboli are formed downstream of the filter, i.e., thefilter itself can be an emboli generator, thus markedly reducing itseffectiveness. Accordingly. blood filters designed to achieve thedesirable objectives of those presently available and to obviate suchdisadvantages are desired.

lt is an object of the present invention to provide an improved bloodfilter. It is another object of the invention to provide an effectiveblood filter having improved compatibility with human blood. These andother objects of the invention will be apparent from the followingdetailed description when read in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a sectional view through a blood filter embodying variousfeatures of the invention; and

FIG. 2 is a diagrammatic view illustrating a blood treatment systemwhich utilizes the blood filter shown in FIG. 1.

It has been found that, by utilizing a packed bed of particles having animpermeable carbon surface, a filter device can be constructed whichdoes an excellent job of removing undesirable debris and microembolifrom blood. However, because of the inherent compatibility ofimpermeable carbon with the components of human blood, a filterconstructed in this manner causes no adverse effects in blood being sotreated and re duces the rate of nucleation of'new emboli downstream ofthe filter.

Shown in HO. 1 is an illustrative blood filter 11 which includes ahousing made from an upper cap 13 and a lower body 15. The illustratedhousing is formed from glass, and the two parts l3, 15 are suitablyjoined together at their interface by adhesive or by suitable mechanicalmeans so as to create an internal, closed chamber 17 of a generalcylindrical shape, the horizontal cross-section of which chamber iscircular. Instead of forming the housing parts from glass, a suitablemetal such as stainless steel could be used, in which case interiorchamber-forming surface would be coated with impermeable vapor-depositedcarbon.

An entrance conduit 19 is provided in the upper cap 13 of the housing,and an exit conduit 21 is provided in the lower body 15. A vent conduit23 is also provided in the cap of the housing to which a suitable checkvalve 25 can be attached which will permit the escape of air or othergases from the chamber 17 while precluding flow thereinto in theopposite direction.

The filtration effect of the blood filter 11 is performed by a bed ofcarbon particles 27 which are supported within the chamber 17 between alower screen 29 and an upper screen 31. The screens 29, 31 are suitablyheld in place either adhesively, or by any other suitable means, forexample, by grooving the internal wall of the chamber 17. The lowerscreen 29 is spaced from the bottom of the chamber 17 a sufficient distance to create a lower plenum 33 wherein the filtered blood can collectand flow smoothly to the exit conduit 21. The upper screen 31 ispreferably also spaced slightly below the top of the chamber 17,creating an upper plenum 35 so that the incoming blood can be fed to theentire upper horizontal surface of the particle bed 27. The screens 29and 31 are made of suitable materials which are compatible with blood,such as stainless steel wire that has been coated with vapordepositedimpermeable carbon.

The carbon particle bed which effects the filtering is made up ofparticles 27, preferably spheroids, having an outer impermeable carbonsurface. Pyrolytic carbon is created by the thermal destruction of acarboncontaining compound, usually a hydrocarbon, in vapor form;however, carbon coatings can also be deposited by vapor-depositionwithout such destruction by using ion-plating or the like, as where acarbon atmosphere is created under very low pressure conditions usingelectron beam heating. For purposes of this application, suchvapor-deposited carbon is considered to be impermeable if it has densityequal to at least about of its theoretical maximum density (or at leastabout 1.55 grams per cm for substantially pure carbon). Glassy orvitreous carbon is inherently impermeable and may be employed at lowerdensities. The size of the carbon particles 27 may vary between about 50microns and 1,000 microns; however, preferably, spheroids between aboutand 500 microns are employed. Spheroids in this size range provide atortuous path between them through which the blood must flow to traversethe filter from the inlet 19 to the outlet 21, and undesirablemicroemboli are removed as the blood flows along this tortuous path.

The particles 27 can be glassy carbon beads of the aforementioned sizerange, or they may be made from grains of suitable material which havebeen coated with pyrolytic or non-pyrolytic carbon by a vapor depositionprocess. lt is important that the carbon particles are smooth, andpolishing may be effected by tumbling or the like to remove any surfaceroughness. Inasmuch as the grains will be totally encapsulated" withinthe impermeable carbon, any suitable material can be employed which isstable at the temperatures at which the vapor deposition coating willtake place, usually be tween about l200C. and 2000C. Zirconium oxidespheroids are readily available and are often employed; however, otherrefractory materials, such as graphite,

silica, and the like, may be used. In the blood-filtering process, thecarbon coatings are not subjected to significant stress and thus do notrequire structural strength, and both laminar carbons and isotropiccarbons, which can be vapor-deposited at relatively low temperatures,e.g., 1200C. to 1600C., are considered to perform satisfactorily.

FIG. 2 illustrates one illustrative system wherein the blood filter 11might be employed. Diagrammatically illustrated is a blood treatmentapparatus 39, which might be a heart-lung machine or the like. Theheartlung machine 39 would be fed with blood by suitable blood pump 41which draws its suction from a reservoir 43. The reservoir 43 has aninlet line 45 which may be connected to the human body from which theblood is being drawn; however, the line 45 might also be branched toprovide for a subsidiary supply of blood from a blood bank, should it beneeded. The heart-lung machine 39 would discharge the blood to theentrance 19 to the blood filter 11, wherein the blood would percolatedownward through the carbon particle bed 27. The filtered blood leavesthrough the outlet 21 and is returned to the human body through the line47, driven by the pressure head supplied by the pump 41.

The illustrated blood filter 11 is made from a glass body wherein achamber 17 is formed, the internal diameter of which measures aboutthree inches. The chamber 17 includes a packed bed of carbon particles27 having a depth of about 2 inches. The particles are spheroids ofzirconium oxide which have been coated with an outer coating ofvapor-deposited pyrolytic carbon, the thickness of the coating averagingabout 50 microns. The ZrO spheroids were coated using a mixture ofpropane and argon at atmospheric pressure (about 40 volume percentpropane) and at a temperature of about 1300C. to produce isotropicpyrolytic carbon having a B.A.F. of 1.1 and a density of about 2 gramsper cm. After coating, the particles are tumbled to remove any surfaceroughness.

The coated zirconium oxide particles range in size from about 80 micronsto about l microns and are supported upon a lower screen of stainlesssteel wire coated with vapor-deposited carbon having the screen openingsmeasuring about 25 microns. The upper screen 31 is made of similarmaterial and is formed to have openings of about 75 microns.Accordingly, the upper screen serves to remove relatively large emboliaggregates from the incoming bloodstream, for example, those over 200microns in size, leaving the carbon particle bed to remove the remainingmicroemboli. The blood filter 11 is, of course, designed to be adisposable item which would not be reused after the operation with aparticular patient is completed.

Although the invention has been described with regard to a blood filterof one particular construction, it

Lil

should be understood that modifications as would be obvious to onehaving the ordinary skill of the art may be made without deviating fromthe scope of the invention which is set forth in the appended claims.For example, the vapor-deposited pyrolytic carbon which is employed tocoat the particles, the screens, and perhaps the interior of the bloodfilter chamber, may be alloyed with a minor amount of a carbide-formingmetal or metalloid, for example, silicon, to give added strength to thecarbon surface, in a manner that is known in the coating art. Additionalfeatures of the invention are set forth in the claims which follow.

What is claimed is:

l. A device for treating human blood prior to its return to a livinghuman body, which device comprises a housing having a chamber formedtherein, entrance means and exit means communicating with said chamber,and a bed of particles disposed in said chamber so that a liquid mustpass through said bed in order to travel from said entrance to saidexit, said particle bed being made up of individual particles betweenabout and 1,000 microns in size, the outer surface of said particlesbeing smooth and formed of impermeable carbon having a density equal toat least about percent of its theoretical maximum density.

2. A device in accordance with claim 1 wherein said particles arespheroids between about 100 and about 500 microns in size.

3. A device in accordance with claim 1 wherein said bed of particles issupported in said chamber between a pair of screens.

4. A device in accordance with claim 3 wherein said housing is formedwith said entrance means and a vent in the upper portion thereof andwith said exit means in the lower portion thereof.

5. A device in accordance with claim 4 wherein a bottom plenum chamberis provided between the lower supporting screen and said exit means.

6. A device in accordance with claim 3 wherein said screens are coatedwith vapor-deposited carbon.

7. A device in accordance with claim 3 wherein the screen which isdisposed between said entrance means and said particle bed has openingsnot greater than about microns in size.

'8. A device in accordance with claim 1 wherein said particles havevapor-deposited carbon coatings.

9. A device in accordance with claim 1 wherein said particles havepyrolytic carbon coatings.

10. A device in accordance with claim 1 wherein the outer surface ofsaid particles is made of glassy carbon.

ILA device in accordance with claim 1 wherein the surface of saidhousing which forms said chamber is coated with vapor-deposited carbon.

* l l= =l

1. A DEVICE FOR REATING HUMAN BLOOD PRIOR TO ITS RETURN TO A LIVINGHUMAN BODY, WHICH DEVICE COMPRISES A HOUSING HAVE A CHAMBER FORMEDTHEREIN, ENTRANCE MEANS AND EXIT MEANS COMMUNICATING WITH SAID CHAMBER,AND A BED OF PARTICLES DISPOSED IN SAID CHAMBER SO THAT A LIQUID MUSTPASS THROUGH SAID BED IN ORDER TO TRAVEL FROM SAID ENTRANCE TO SAIDEXIT, SAID PARTICLE BED BEING MADE UP OF INDIVIDUAL PARTICLES BETWEENABOUT 50 AND 1000 MICRONS IN SIZE, THE OUTER SURFACE OF SAID PARTICLESBEING SMOOTH AND FORMED OF IMPERMEABLE CARBON HAVING A DENSITY EQUAL TOAT LEAST ABOUT 70 PERCENT OF ITS THEORETICAL MAXIMUM DENSITY.
 2. Adevice in accordance with claim 1 wherein said particles are spheroidsbetween about 100 and about 500 microns in size.
 3. A device inaccordance with claim 1 wherein said bed of particles is supported insaid chamber between a pair of screens.
 4. A device in accordance withclaim 3 wherein said housing is formed with said entrance means and avent in the upper portion thereof and with said exit means in the lowerportion thereof.
 5. A device in accordance with claim 4 wherein a bottomplenum chamber is provided between the lower supporting screen and saidexit means.
 6. A device in accordance with claim 3 wherein said screensare coated with vapor-deposited carbon.
 7. A device in accordance withclaim 3 wherein the screen which is disposed between said entrance meansand said particle bed has openings not greater than about 75 microns insize.
 8. A device in accordance with claim 1 wherein said particles havevapor-deposited carbon coatings.
 9. A device in accordance with claim 1wherein said particles have pyrolytic carbon coatings.
 10. A device inaccordance with claim 1 wherein the outer surface of said particles ismade of glassy carbon.
 11. A device in accordance with claim 1 whereinthe surface of said housing which forms said chamber is coated withvapor-deposited carbon.